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  • 1
    Electronic Resource
    Electronic Resource
    Comparative studies on the adsorption and association of 3-methylxanthine and 7-methylxanthine at a charged interface (1996)
    Springer
    Monatshefte für Chemie 127 (1996), S. 609-619 
    Details
    ISSN: 1434-4475
    Keywords: Adsorption ; Association ; AC voltammetry ; Methylxanthines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Eine systematische vergleichende Untersuchung zur Adsorption und Assoziation von 3-Methylxanthin (3MXan) und 7-Methylxanthin (7MXan) an Quecksilber-Lösungs-Grenzflächen wurde mittels AC-Voltammetrie in sauren, neutralen und basischen Pufferlösungen durchgeführt. Oberhalb einer bestimmten Grenzkonzentration kommt es durch Wechselwirkungen zwischen vertikal angeordneten3MXan-Molekülen zu einer langsamen Reorientierung umE ecm, was zu einer senkrechten Anordnung führt. Die Assoziation von7MXan ist gehindert und erlaubt daher keine ausgeprägten Basen-Basen-Wechselwirkungen. Die erhöhte Oberflächenaktivität von3MXan gegenüber7MXan resultiert aus der unterschiedlichen Stellung der Methylgruppe am Purinrest. Der Effekt einiger zweiwertiger Metallionen auf die Adsorption und Assoziation von3MXan und7MXan wurde untersucht. Die Ergebnisse weisen auf eine Begünstigung der Wechselwirkungen hin; die Bildung von vertikal angeordneten Grenzschichten an der Elektrodenoberfläche sollte daher im Fall vonM(II)-Mxan-Komplexen erleichtert sein. Die Adsorptionsparameter der untersuchten Verbindungen wurden in Abwesenheit und in Gegenwart von Cu(II) bei verschiedenenpH-Werten berechnet. Die Ergebnisse werden mit dem Verhalten von Xanthin verglichen.
    Notes: Summary A systematic comparative study of the adsorption and association of 3-methylxanthine (3MXan) and 7-methylxanthine (7MXan) at mercury-solution interfaces in acidic, neutral, and alkaline buffer solutions was undertaken by ac voltammetry. At bulk concentrations of3MXan above a threshold value, the stacking interactions between vertically oriented molecules lead to a slow reorientation aroundE ecm, and the molecules adopt a perpendicular orientation. The association of the adsorbed molecules of7MXan is hindered and is not effective in promoting base-base stacking interactions. The enhanced surface activity of3MXan compared to7MXan results from the different position of the methyl group in the purine moiety. The effect of some divalent metal ions on adsorption stages and association of the investigated compounds has been studied. The results indicate that the complexation of methylated xanthine enhances the stacking interactions and hence would be expected to facilitate the formation of perpendicularly stacked layers ofM(II)-MXan complexes on the electrode surface. The adsorption parameters of the investigated compounds have been computed in absence and presence of Cu(II) at differentpH values. The results are compared with the behaviour of xanthine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00817253
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  • 2
    Electronic Resource
    Electronic Resource
    Surface activity and orientation of inosine at a mercury/solution interface (1997)
    Springer
    Monatshefte für Chemie 128 (1997), S. 827-836 
    Details
    ISSN: 1434-4475
    Keywords: Surface activity ; Orientation ; AC voltammetry ; Inosine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Adsorption und Assoziation von Inosin an einer Quecksilbertropfelektrode wurde mittels phasensensitiver AC-Voltammetrie systematisch untersucht. Die Abhängigkeit des Adsorptionsgleichgewichts von Parametern wiepH-Wert, Adsorptionspotential, Adsorptionszeit und Inosinkonzentration wurde gemessen. Dabei zeigte sich, daß die Assoziation der adsorbierten Spezies vorwiegend von der Anordnung und den Wechselwirkungen der neutralen Inosinmoleküle abhängt. Inosin bildet über einen weiten Potentialbereich eine dünne Adsorptionsschicht aus, wobei die Base flach auf der Elektrodenoberfläche aufliegt. Ab einem bestimmten Grenzwert der Konzentration tritt eine Reorientierung zu einer senkrechten Anordnung ein. Keimbildung und Wachstumsmechanismus wurden mittels derAvrami-Gleichung analysiert. Eigenschaften und Adsorptionsparameter der verdünnten und der kompakten Inosinschicht konnten aus der zweistufigenFrumkin-Isotherme und aus der Potentialabhängigkeit der Adsorption bestimmt werden.
    Notes: Summary A systematic investigation on the adsorption and association of inosine at a hanging mercury drop electrode by phase-sensitive ac voltammetry has been performed. The adsorption equilibrium bas been determined as a function of various parameters such aspH, adsorption potential, adsorption time, and bulk concentration of inosine. It was found that the association of the adsorbed species depends predominantly on the stacking interactions of neutral inosine molecules. Over a wide potential range, inosine exhibits a dilute adsorption characteristic where it is adsorbed with the base flat on the electrode surface. Above a certain threshold value, inosine appears to undergo a surface reorientation and adopts a perpendicular position. The nucleation and growth mechanism is analyzed applying theAvrami equation. Characteristic properties and adsorption parameters of dilute and compact layers of inosine were evaluated from the two-stepFrumkin isotherm and from the potential dependence of adsorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807092
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  • 3
    Electronic Resource
    Electronic Resource
    Differential pulse polarographic determination of 1-methyladenine, deoxyadenosine, deoxyadenosine-5′-monophosphate and dinucleotides of adenine (1987)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 326 (1987), S. 146-149 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary 1-Methyladenine, deoxyadenosine (deoxy-A), deoxyadenosine-5′-monophosphate (deoxy-5′-AMP), adenylyl-(3′→5′)-adenosine (APA) and adenylyl-(3′→5′)-guanosine (APG) were studied at various pH-values by differential pulse polarography at the dropping mercury electrode. The applicability of differential pulse polarography for the trace determination of the investigated biological compounds was also examined with regard to the dependence of differential pulse current on various parameters such as pH, pulse amplitude, scan rate and drop time. Detection limits are: 1-methyladenine 0.9 μM; deoxy-A 0.93 μM, deoxy-5′-AMP 1.8 μM, APA 0.93 μM and APG 0.91 μM. The validity of this method is supported by the constancy of the i dpp/C-values and a statistical analysis is included on calibration curve parameters and observed concentrations.
    Notes: Zusammenfassung 1-Methyladenin, Desoxyadenosin (Desoxy-A), Desoxyadenosinmonophosphat (Desoxy-5′-AMP) Adenylyl-(3′→5′)-adenosin (APA) und Adenylyl-(3′→5′)-guanosin (APG) wurden bei verschiedenen pH-Werten mit Hilfe der Differentialpuls-Polarographie an der Quecksilbertropfelektrode untersucht. Die Anwendbarkeit dieser Methode zur Spurenbestimmung der Verbindungen wurde ebenfalls im Hinblick auf die Abhängigkeit des Differentialpuls-Stromes von unterschiedlichen Parametern (pH, Pulsamplitude, Scanrate, Tropfzeit) geprüft. Folgende Nachweisgrenzen wurden gefunden: 0,9 μM für Methyladenin, 0,93 μM für Desoxy-A, 1,8 μM für Desoxy-5′-AMP, 0,93 μM für APA und 0,91 μM für APG. Die Konstanz der i dpp/C-Werte zeigt die Anwendbarkeit der Methode. Die Parameter der Eichkurven und die entsprechenden Konzentrationen werden statistisch betrachtet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00468500
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  • 4
    Electronic Resource
    Electronic Resource
    Adsorptive stripping analysis of thiocytosine at the static mercury electrode surface (1992)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 342 (1992), S. 601-605 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The cathodic adsorptive stripping method has been applied for the trace determination of thiocytosine (Tcyt) using differential pulse voltammetry at the HMDE. The strong interaction of Tcyt with the mercury electrode surface leads to the formation of an adsorbed film of Hg(II)-thiolate complex at the electrode surface. The formation of this film is followed by cyclic DC- and differential pulse voltammetry. It has been found that formation of such film depends on various parameters, e.g. pH, concentration, adsorption time and adsorption potential. The influence of these parameters on the shape and the peak height of the cathodic stripping peak during the negative scan of potential has been determined. The influences of anions (SO 4 2− , Cl−, ClO 4 − , NO 3 − ) and cations [Cu(II), Ni(II), Pb(II) and Cd(II)] on the method of analysis are considered. The calibration curve for the determination of Tcyt is linear and the detection limit is 1.49×10−8 mol/l, whereas in the presence of Cu(II) the method is developed and the detection limit for Tcyt determination is lowered to 4.99×10−9 mol/l. A statistical analysis of the calibration curve data is included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00321921
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  • 5
    Electronic Resource
    Electronic Resource
    Cathodic adsorptive stripping voltammetry of 6-thiopurine in absence and presence of some metal ions (1993)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 345 (1993), S. 733-736 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Cathodic stripping voltammetry of an adsorbed 6-thiopurine at HMDE was investigated in solutions of varying pH. A rapid and sensitive differential pulse voltammetric method was selected for its trace determination. A method has also been developed for the determination of 6-thiopurine in presence of Cu(II), due to the strong adsorption of the Cu-6-thiopurine complex at the surface of the HMDE and subsequent reduction of the surface-bound complex. A detection limit of 9.9×10−9 mol/l was achieved in presence of Cu(II) and the slope of the straight line was seven times the slope in absence of Cu(II). Cathodic adsorptive stripping (CAS) voltammetry of 6-thiopurine in presence of Ni(II), Pb(II), Cd(II), and Fe(III) was also investigated. The influence of several operational parameters has been considered. Statistical analysis of the calibration curve data is included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00325845
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  • 6
    Electronic Resource
    Electronic Resource
    Differential pulse polarographic determinations of iodate, bromate and periodate (1980)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 301 (1980), S. 414-416 
    Details
    ISSN: 1618-2650
    Keywords: Best. von Bromat, Iodat, Periodat ; Polarographie, Differentialpuls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary The application of differential pulse polarography for quantitative trace determination of iodate, periodate and bromate has been investigated. Optimum conditions were found (pulse amplitude 100 mV, scan rate 2 mV s−1, drop time 2 s). The detection limit for IO 3 − , BrO 3 − and IO 4 − is ca. 2.4×10−6M at pH 3 whereas at pH 9.3 the reduction of IO 3 − and IO 4 − gave concentration sensitive peak heights down to 9.9 ×10−7M. A differential pulse polarographic method has been developed for the simultaneous determination of iodate-bromate or periodate-bromate.
    Notes: Zusammenfassung Optimale Bedingungen zur Bestimmung dieser Ionen im Spurenbereich wurden ausgearbeitet (Pulsamplitude 100 mV, Scangeschwindigkeit 2 mV s−1, Tropfzeit 2 s). Die Nachweisgrenze für die drei Ionen liegt bei 2,4 · 10−6 M für pH 3. Bei pH 9,3 ergaben sich für Iodat und Periodat konzentrationsabhängige Peakhöhen bis herab zu 9,9 · 10−7 M. Da der Bromatpeak bei wesentlich negativerem Potential auftritt als der Iodat bzw. Periodatpeak konnten Iodat und Bromat bzw. Periodat und Bromat nebeneinander bestimmt werden.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00475749
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  • 7
    Electronic Resource
    Electronic Resource
    Studies on the kinetics of the Hydrolysis of Some Substituted Benzylidene Benzoichydrazide with differential pulse polarography (1986)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 328 (1986), S. 841-848 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the hydrolysis of some substituted benzylidene benzoichydrazide 1a-e in 40% (v/v) ethanol buffer mixture have been investigated by differential pulse polarography. The mechanism of the hydrolysis in acidic buffer solutions is discussed.The catalysis by H⊕ involves the conversion of the hydrazide compound to its conjugated acid in a rapid preequilibrium step followed by a slow attack of water. The effects of pH, water, organic solvents and molecular structure on the reaction rate and the activation are investigated.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19863280525
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  • 8
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    Differential pulse polarographic determinations of iodate, bromate and periodate (1980)
    Springer
    Details
    Publication Date: 1980-01-01
    Print ISSN: 0016-1152
    Topics: Chemistry and Pharmacology
    Published by Springer
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  • 9
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    Cross-disciplinary evolution of the genomics revolution (2018)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2018-08-16
    Description: Born out of the Human Genome Project (HGP), the field of genomics evolved with phenomenal speed into a dominant scientific and business force. While other efforts were intent on estimating the economic impact of the genomics revolution, we shift focus to the social and cultural capital generated by bridging together biology and computing—two of the constitutive disciplines of "genomics". We quantify this capital by measuring the pervasiveness of bio-computing cross-disciplinarity ( XD ) in genomics research during and after the HGP. To provide interlocking perspectives at the career and epistemic levels, we assembled three data sets to measure XD via (i) the collaboration network between 4190 biology and computing faculty from 155 departments in the United States, (ii) cross-departmental affiliations within a comprehensive set of human genomics publications, and (iii) the application of computational concepts and methods in research published in a preeminent genomics journal. Our results show the following: First, research featuring XD collaborations has higher citation impact than other disciplinary research—an effect observed at both the career and individual article levels. Second, genomics articles featuring XD methods tend to have higher citation impact than epistemically pure articles. Third, XD researchers of computing pedigree are drawn to the biology culture. This statistical evidence acquires deeper meaning when viewed against the organizational and knowledge transfer mechanisms revealed by the data models. With cross-disciplinary initiatives set to dominate the agenda of funding agencies, our case study provides a framework for appreciating the long-term effects of these initiatives on science and its standard-bearers.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    Time-Resolved Characterization of the Formation of a Collisionless Shock (2013)
    American Physical Society (APS)
    Details
    Publication Date: 2013-05-15
    Description: Author(s): H. Ahmed, M. E. Dieckmann, L. Romagnani, D. Doria, G. Sarri, M. Cerchez, E. Ianni, I. Kourakis, A. L. Giesecke, M. Notley, R. Prasad, K. Quinn, O. Willi, and M. Borghesi We report on the temporally and spatially resolved detection of the precursory stages that lead to the formation of an unmagnetized, supercritical collisionless shock in a laser-driven laboratory experiment. The measured evolution of the electrostatic potential associated with the shock unveils the ... [Phys. Rev. Lett. 110, 205001] Published Tue May 14, 2013
    Keywords: Plasma and Beam Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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